Typically, there are cases where rotary, machines represented by compressors and steam turbines become unable to continue operation because a fluid-like, unstabilizing force produced under specific conditions of use causes their spindle shafts to vibrate unstably. To prevent such an unstable vibration, efforts are made to optimize the bearing characteristic (vibration characteristic) so as to make the spindle shafts stable under all the conditions of use in consideration of the unstabilizing force. The optimization of the vibration characteristic is performed by adjusting the clearance, preload, or the like of the bearing. However, the clearance, preload, or the like is heavily influenced by the dimensional tolerance or erection tolerance of the bearing. Therefore, there are cases where the clearance or preload of the bearing actually fabricated fails to offer the target vibration characteristic, leading to production of an unstable vibration.
To suppress such unstable vibration, there is adopted a squeeze film damper for applying additional damping to the vibration of the spindle shaft to produce stabilization. The squeeze film damper is provided on the shaft end that extends externally from the bearing. The squeeze film damper effectively damps the vibration of the spindle shaft by use of a squeeze film (oil film) formed around the outer circumference of the shaft end. Thereby, the squeeze film damper suppresses the unstable vibration of the spindle shaft.
Patent Document 1 discloses one example of a damper structure utilizing such a squeeze film.